In traditional shingle manufacturing, a glass mat web or other substrate is moved in a downstream direction past various stations of a manufacturing line. At one station, the glass mat is saturated with molten liquid asphalt to form a moisture barrier. The saturated substrate is then coated with top and/or bottom coats of asphalt prior to application of protective granules and cutting to form individual shingles. Multiple shingles may be cut across the width of the web. Prior art coating processes in shingle manufacturing typically utilize a roll coating technique, wherein a coating material such as molten asphalt is pumped into a puddle in front of a coating roller. The substrate is conveyed through the coating puddle into a nip roll, which meters the amount of coating applied to the substrate. The roll holds back excess coating material, which pours into a pan and back to a surge tank to be recirculated back to the puddle.
The above technique has been used for many years and works well at line speeds, i.e. the speed of the moving web in the downstream direction, up to about 850 feet per minute. However, the technique exhibits inherent limitations at line speeds higher than this, making it unsuitable for high speed shingle manufacturing above 850, and more specifically above 1000, feet per minute. The coating step in shingle manufacturing has thus become a limiting link in the chain when attempting to increase line speeds in shingle manufacturing plants above traditional speeds. Further, so much molten asphalt in the traditional puddle and roller technique generates fumes and smoke that can become a health hazard for plant workers.
A need exists for a method and apparatus for saturating and coating a moving web of substrate material in shingle manufacturing at line speeds of 1000 feet per minute and higher while maintaining a desired and consistent thickness and saturation of the coating material. A further need exists for a method and apparatus that enables application of multiple layers coating materials and different coating materials and profiles on the top and bottom of the web. It is to such a method and apparatus that the present invention is primarily directed.